In the production of aluminium (aluminium smelters) or melting of aluminium (eg. for manufacture of extrusions, ingots and billets) a by-product called aluminium dross is formed. Such a by-product is formed in molten aluminium in view of oxygen from environmental air as well as impurities present in aluminium. Aluminium dross generally comprises free metal and non-metallic substances (e.g. aluminium oxide and salts). Aluminium nitrides and carbides may also be present, as well as metals oxides derived from molten alloy. Aluminium dross does represent an interesting by-product to valorize in order to recuperate or recover the products contained therein.
It is known to process the dross first by separating aluminium from it to obtain aluminium dross residues, which are also known as non-metallic products (NMP). In other words it can be said that the aluminium dross residues are obtained by at least partially removing aluminium metallic from aluminium dross. Aluminium dross is normally treated either by a plasma or in a conventional furnace with a salt mixture, to remove recoverable aluminum metal, leaving a dross residue having reduced aluminum content.
The main components in aluminium dross residues generally include alumina, aluminum metallic and spinel. Other main components such as aluminum nitride, gibbsite (Al(OH)3), and diaoyudaoite (NaAl11O17) can also be present. Various minor components such as Fe2O3, SiO2, MgO can also be present.
Dube et al. in U.S. Pat. Nos. 4,959,100 and 4,960,460 disclose treatment processes for recovering aluminum from aluminum dross hence producing aluminum dross residues. Such aluminium dross residues are also disclosed in U.S. Pat. No. 5,407,459, and known as NOVAL™.
Formerly aluminium dross residues originating from known dross processing techniques in rotating salt furnaces were put in a landfill as waste. Such disposal is increasingly facing environmental problems or is even banned, since salts can leach from the aluminium dross residues and pass into the soil below. Aluminum dross residues are frequently classified as hazardous material. Therefore, the disposal, transformation or valorization of the aluminium dross residues is of prime economic and environmental importance.
Several solutions have been proposed for recuperating aluminium from aluminium dross but only few have been proposed for valorizing or treating aluminium dross residues i.e. residues that are obtained after removal of aluminium from aluminium dross.
It would thus be highly desirable to be provided with a process that would propose an alternative way for valorizing aluminium dross residues into a product, which is different than calcium aluminates.